Finite Impulse Response Filter Design - Digital Signal Processing: Fundamentals and Applications - page 250

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FIGURE 7.19B

Spectral comparison of the original speech and processed speech using the bandpass filter.

EXAMPLE 7.11
Design a bandstop FIR filter with the following specifications:

Lower cutoff frequency 1,250 Hz
Lower transition width 1,500 Hz
Upper cutoff frequency 2,850 Hz
Upper transition width 1,300 Hz
Stopband attenuation 60 dB
Passband ripple 0.02 dB
Sampling rate 8,000 Hz

Solution:
We can directly compute the normalized transition width:

Df 1 ¼ 1;500=8;000 ¼ 0:1875 and Df 2 ¼ 1;300=8;000 ¼ 0:1625

The filter lengths are determined using the Blackman windows as
N 1 ¼ 5:5=0:1875 ¼ 29:33;

and N 2 ¼ 5:5=0:1625 ¼ 33:8